1. Field of the Invention
The present invention relates to an electrophotographic development process to prepare printed matters on a copying machine, a printer or a facsimile, wherein an electrostatic latent image on a photosensitive substance is developed with a developer which is a mixture of toner and carriers having different shape and properties, and is formed into magnetic brush by a magnetic field source device, and the toner image is transferred to transfer members such as ordinary paper and resin film and is thereafter fixed.
2. Description of the Prior Art
Electrophotographic development processes are roughly classified into four types;
(1) 2-component development process using carrier such as iron powder and non-magnetic toner, wherein direct current voltage is applied between a photosensitive substance and a non-magnetic and a conductive cylindrical sleeve as a developer conveyer.
(2) 1-component development process using magnetic toner, wherein alternating current voltage and/or direct current voltage are applied between a photosensitive substance and a sleeve.
(3) so-called 1,5-component development process using resin carrier and magnetic toner, wherein direct current voltage is applied between a photosensitive substance and a sleeve, with both the sleeve and a magnet built therein rotated.
(4) so-called new 2-component development process using spherical ferrite carriers and magnetic toner, wherein direct current voltage is applied between a photosensitive substance and a sleeve, with both the sleeve and a magnet built therein rotated.
Those four processes have their own characteristics as follows;
(1) The 2-component development process was established earliest, wherein carrier and toner are mixed by the specified ratio and the toner is charged into specified polarity by frictional charging to deposit them to portions of electrostatic latent images on the photosensitive substance. It is a favorable process because the copy is easy to perform, and it is suitable for color printing, which tends to prevail lately, since it uses toner containing no magnetic materials. However, there are the following problems: as a stirring means and a toner concentration monitor are necessary to charge the toner and the carrier in good conditions and to control the concentration of the developer consumed toner to be uniform, a large-sized and complicated development device is needed, resulting in cost increase; as carrier which has been used for specified duration deteriorate, it must be exchanged; as iron carrier is flake-like and poor in fluidity, it tends to require a high power driving system.
(2) A process for using conductive magnetic toner was devised for the 1-component development process in order to solve the problem on stabilization of the toner concentration by using the stirrer, which is a disadvantage of the 2-component development process. However, this is unappropriate because the images on the matters from using a photosensitive substance repeatedly, which is desired in nature, are obsure, even if the printing matters can be directly obtained. Accordingly, a process in which insulative magnetic toner is used to solve those problems, has been established to obtain, under the same sensitivity body potential conditions as those of the 2-component development process, clear images by devising such toner as is added with charging control agents inside or outside the toner. However, as the charging quantity improved, there were inconveniences that charging cohesion of the toner arose easily to cause the toner deposit on a toner regulating plate, which brought about white lines in the images from development deficiency due to toner deficiency.
By the way, a process for employing, as development bias voltage, voltage obtained by piling up alternating current voltage on the alternating current voltage or the direct current voltage, is known as a so-called jumping process. It is a one step advanced process than that for applying only direct current voltage, since magnetic brush formed by a developer does not directly contact with a photosensitive substance and the development is carried out by toner clouds generated by toner oscillation caused by the alternating current component of the bias voltage, which is capable of obtaining clear images. However, like an ordinary 1-component development process using direct current voltage as the bias voltage, this process has to be raised in accuracy of dimensions and shape of a sleeve as a developer conveyer so as to quantify an amount of charging and an amount of toner. In addition, the process bears production difficulties such as requiring uniformity of the surface unevenness created by sand blast, which lead to high production cost, and also bears problems of generating the white line due to the toner cohesion.
(3) The so-called 1.5-component process using resin carrier was devised to avoid damages due to scratching the surface of a photosensitive substance with carrier, which is a problem of the 2-component development process, and to prevent the deterioration of image quality due to the carrier deposition. That is, damages or short life of the photosensitive substance, caused by carrier intensively scratching the surface of the photosensitive substance is not only prevented, but also image quality deterioration due to existence of light spots in black image portions from the carrier deposition, can be avoided by employing resin carrier with the same component in nature as that of the toner, so as to come to the same phenomenon as the toner deposition upon the images even if the carrier deposition takes place. However, this is basically of a 2-component system, and thus density irregularity arises, unless a mixing ratio between the carrier and toner is within the specified values. Especially, when a stirrer is not employed and high density printing matters are continuously intended to be obtained, an amount of toner consumed increases greatly to thus result in the density drop.
(4) The so-called new 2-component development process using spherical ferrite carriers was devised to prevent charging cohesion which arises with an increase in charge amount of insulate toner, and to solve dropout due to toner deficiency upon development, which are problems associated with 1-component development process using magnetic toner. This process is effective for preventing the charging cohesion, but as described in Japanese Patent Non-examined Publication No. 59-182464 and U.S. Pat. No. 4,640,880, in order to obtain a favorable image, it is necessary to rotate both of a cylindrical sleeve and a magnet built therein and, especially, it is necessary to rotate them reversely with each other and, moreover, to make a conveyance direction of the toner the same with a moving direction of the photosensitive substance. This results in cost increase from needing a high power driving system to rotate a magnet with large mass at high speed, gears to transmit the driving force and costly rolling bearings to get smooth rotation. In addition, wrong balancing gives rise to vibration to cause noise.